Leadless package for high current devices

ABSTRACT

Some exemplary embodiments of a direct contact leadless package and related structure and method, especially suitable for packaging high current semiconductor devices, have been disclosed. One exemplary structure comprises a first contact lead frame portion, a paddle portion, and an extended contact lead frame portion held together by a mold compound. A first semiconductor device is attached to a top side of the paddle portion and is enclosed by said mold compound, while a second semiconductor device is attached to a bottom side of said paddle portion and is in electrical contact with said the first semiconductor device. The extended contact lead frame portion is in direct electrical contact with the second semiconductor device without using a bond wire. Alternative exemplary embodiments may include additional extended lead frame portions, paddle portions, and semiconductor devices in various configurations.

This is a divisional of application Ser. No. 12/583,991 filed Aug. 28,2009 now U.S. Pat. No. 7,994,615.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor devicepackages. More particularly, the present invention relates to leadlesssemiconductor packages.

2. Background Art

Packages are required in the integrated circuit (IC) industry to providehousing for semiconductor devices and circuits, to provide mechanicalstrength, stability, and reliability, and to prevent damage tosemiconductor devices and circuits. Packages are also required to havesmall form factors, good heat dissipation capability, electrical leadsor other electrical connections that do not significantly add toinductance and resistance in signal paths. These packaging requirementsshould be achieved at a reasonable cost, since semiconductor packagesmight end up costing much more than the semiconductor devices andcircuits that are housed within.

The packaging of power transistors and devices requires meetingadditional and unique challenges, including not only a reduced formfactor, but also a high current carrying capability, as well as a highreliability standard. Moreover, packages for power transistors anddevices should be relatively simple to produce since only a fewtransistors or devices are housed in each package and, therefore, agreater portion of the cost of the final product is the package itself.

Previous solutions have relied on, for example, complex wire bondtechnology for various terminals of power transistors or power devicesthat have resulted in reduced reliability and increased packagingcomplexity, while not accommodating high current carrying capability andlow form factor requirements of power transistors and devices. Moreover,closely packed power transistors housed along with their controlintegrated circuits (control ICs) have exacerbated the problemsassociated with efficient packaging of power transistors and devicesnext to control ICs interfacing and controlling the power transistorsand devices. Thus, a unique solution resulting in high current carryingcapability, efficient and dense packaging, and low form factor isneeded.

SUMMARY OF THE INVENTION

A direct contact leadless package for high current devices,substantially as shown in and/or described in connection with at leastone of the figures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to an initialstep of packaging.

FIG. 1B illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to anintermediate step of packaging.

FIG. 1C illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to anintermediate step of packaging.

FIG. 1D illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to anintermediate step of packaging.

FIG. 1E illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to anintermediate step of packaging.

FIG. 1F illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to a finalstep of packaging.

FIG. 2A illustrates a cross sectional view of a package in fabricationaccording to an alternative embodiment of the invention, correspondingto an intermediate step of packaging.

FIG. 2B illustrates a cross sectional view of a package in fabricationaccording to the embodiment of the invention in FIG. 2A, correspondingto a final step of packaging.

FIG. 3A illustrates a cross sectional view of a package in fabricationaccording to yet another embodiment of the invention, corresponding toan intermediate step of packaging.

FIG. 3B illustrates a cross sectional view of a package in fabricationaccording to the embodiment of the invention in FIG. 3A, correspondingto a final step of packaging.

DETAILED DESCRIPTION OF THE INVENTION

The present application is directed to a direct contact leadless packagefor high current devices. The following description contains specificinformation pertaining to the implementation of the present invention.One skilled in the art will recognize that the present invention may beimplemented in a manner different from that specifically discussed inthe present application. Moreover, some of the specific details of theinvention are not discussed in order not to obscure the invention. Thespecific details not described in the present application are within theknowledge of a person of ordinary skill in the art.

The drawings in the present application and their accompanying detaileddescription are directed to merely exemplary embodiments of theinvention. To maintain brevity, other embodiments of the invention,which use the principles of the present invention, are not specificallydescribed in the present application and are not specificallyillustrated by the present drawings.

FIG. 1A illustrates a cross sectional view of a package in fabricationaccording to an embodiment of the invention, corresponding to an initialstep of half-etching a lead frame. More specifically, FIG. 1A shows across sectional view of a package in the process of fabrication.Indentations 130 and 134 are formed in lead frame 110, dividing a topside of lead frame 110 into surfaces 120, 122, and 126. For example, ahalf-etching process with an appropriate template might be used to formindentations 130 and 134.

Utilizing the lead frame fabricated in the previous step shown in FIG.1A, during the next step illustrated in FIG. 1B, semiconductor device170, labeled U1, is attached to the top of lead frame 110 on surface122, Semiconductor device 170 may comprise, for example, a controlintegrated circuit (IC) or driver IC to control one or more powertransistors or devices. However, semiconductor device 170 is not limitedto a control IC or driver IC and may comprise other semiconductordevices that can be used to perform various functions, and for examplein conjunction with a power transistor or power device.

FIG. 1C shows a cross sectional view of a package in the process offabrication continuing from FIG. 1B. Bond wire 140 is attached between abonding pad situated on top of semiconductor device 170 and a pad onsurface 120, whereas bond wire 142 is attached between a bonding pad ontop of semiconductor device 170 and a pad on surface 126 (bonding padsare not shown in the drawings). These wire bonds may provide electricalconnections that semiconductor device 170 can use, for example, tocontrol other semiconductor devices. As FIG. 1C is shown as a crosssectional view, additional bond wires (not shown) might also beconnected parallel to bond wires 140 and 142 to provide additionalelectrical connections for semiconductor device 170. Separate bond wiresomitted from FIG. 1C might optionally be connected between the top ofsemiconductor device 170 and surface 122 to provide, for example,current sensing capability for semiconductor device 170 or for providingadditional ground connections for semiconductor 170. Furthermore,alternative methods of providing electrical connections may also be usedinstead of bond wires.

Next, FIG. 1D shows a cross sectional view of a package in the processof fabrication continuing from FIG. 1C. Mold compound 150 is formedaround the package, enclosing semiconductor device 170, bond wires 140and 142, and the top side of lead frame 110. In this manner, theelements of the package can be held together as one modular unit,facilitating simplified integration.

FIG. 1E shows a cross sectional view of the package in the process offabrication continuing from FIG. 1D. Contact lead frame portion 112,paddle portion 114, and extended contact lead frame portion 118 areformed from lead frame 110. For example, an etching process might beused similar to the process used to form indentations 130 and 134 inFIG. 1A, except that the etching process starts from the bottom side oflead frame 110 rather than the top side of lead frame 110, and adifferent template appropriate for the bottom side is used. Thus,existing fabrication processes can be advantageously used in a costeffective manner. Although some portions of lead frame 110 are etchedaway completely such as the areas corresponding to indentations 130 and134, the presence of mold compound 150 keeps the package held together,avoiding the need for a mold tape or a supporting substrate.

As shown in FIG. 1E, contact lead frame portion 112 retains the sameheight as lead frame 110, whereas paddle portion 114 has a reducedthickness relative to lead frame 110 and is effectively raised inposition compared to contact lead frame portion 112. Extended contactlead frame portion 118 has a portion with the same thickness of contactlead frame portion 112 and a remainder portion with the same reducedthickness and raised position as paddle portion 114. As shown by thecross sectional view of FIG. 1E, extended contact lead frame portion 118may thus have the appearance of an L-shaped overhang.

FIG. 1F shows a cross sectional view of a package in the process offabrication continuing from FIG. 1E. Semiconductor device 160, labeledQ1, is attached to the bottom of paddle portion 114 by conductive dieattach, pad, land, solder bumps or balls, or other electrical contactinterface 164. Semiconductor device 160 is also in direct electricalcontact with extended contact lead frame portion 118 by conductive dieattach, pad, land, solder bumps or balls, or other electrical contactinterface 166. After attaching semiconductor device 160, the fabricationof the package is essentially complete and the package may then beattached on top of printed circuit board (PCB) 180 for integration usingconductive die attach, pad, land, solder bumps or balls, or otherelectrical contact interface 168 on the bottom surface of semiconductordevice 160. It should be noted that PCB 180 may extend beyond the crosssection shown in FIG. 1F and may also include other components not shownin FIG. 1F.

Semiconductor device 160 might be, for example, a power transistor,comprising a silicon, silicon germanium, gallium arsenide, galliumnitride, or other III-nitride field effect transistor (FET) or highelectron mobility transistor (HEMT), or any other type of powertransistor or device. In this case, electrical contact interface 166 mayprovide electrical contact to a gate terminal of the power transistor,electrical contact interface 164 may provide electrical contact to asource terminal of the power transistor, and electrical contactinterface 168 may provide electrical contact to a drain terminal of thepower transistor. These are only given as exemplary terminalassignments, and alternative embodiments may arrange terminals asdemanded for particular applications. For example, electrical contactinterface 164 may connect to a drain terminal and electrical contactinterface 168 may connect to a source terminal.

Assuming the terminal assignments provided above, semiconductor device170, for example a control IC, may then control the operation ofsemiconductor device 160, for example a power transistor. As shown inFIG. 1F, semiconductor device 170 is in electrical contact withelectrical contact interface 164 via paddle portion 114, andsemiconductor device 170 is also in electrical contact with electricalcontact interface 166 via bond wire 142 and extended contact lead frameportion 118. Thus, for example, a control IC 170 may apply a voltagebetween electrical contact interface 166 connected to a gate of a powertransistor and electrical contact interface 164 connected to a source ofthe power transistor to control the current flow between the source andthe drain of the power transistor, the drain being connected toelectrical contact interface 168.

Since electrical contact interfaces 164, 166, and 168 are respectivelyin direct contact with paddle portion 114, extended contact lead frameportion 118, and PCB 180, an advantageous and efficient direct contactsystem with a large contact surface area is provided having increasedreliability, reduced resistance and inductance, and greater currentconduction capability. For example, in one embodiment, land grid arrays(LGAs), solder bumps, solder balls, and/or studs might be used forelectrical contact interface 166, whereas LGAs, solder bumps, and/orsolder balls might be used for electrical contact interface 164, andLGAs might be used for electrical contact interface 168. Theseelectrical connection schemes are only provided as examples, and one mayuse any combination of direct contacts as needed in variousapplications.

The large surface area direct contacts provided by electrical contactinterfaces 164, 166, and 168 allow semiconductor device 160 to handlehigh current density and also dissipate heat in an efficient manner byavoiding the longer routes and limited contact areas provided bytraditional interconnect methods such as wire bonds. Since the complexrouting required for wire bonds can be avoided, a reduced package formfactor and footprint may also be achieved. The mechanical simplicity ofthe present invention's package further enhances stability andreliability, and avoids problems such as high stress areas leading tocracked substrates.

Furthermore, the double-sided contacts of semiconductor device 160provide flexible cooling options for efficient heat dissipation. Forexample, thermal vias might be used within PCB 180 to route heat fromsemiconductor device 160 to an external metal chassis, and a top mountedheat sink with forced air cooling might still be mounted above moldcompound 150, allowing concurrent dispersion of heat from both top andbottom sides. If thickness of the package is a greater designconsideration, then the top mounted heat sink may be omitted.

FIG. 2A shows a cross sectional view of a package in the process offabrication according to an alternative embodiment of the invention. Afabrication process as described above and shown in achieving thepackage in FIG. 1E may be used in a similar manner to achieve thepackage shown in FIG. 2A, and is therefore omitted for brevity. However,in contrast to the package shown in FIG. 1E, FIG. 2A provides analternative embodiment for another exemplary package, which differs fromFIG. 1E in that contact lead frame portion 112 is also an extendedcontact lead frame portion 212, similar to extended contact lead frameportion 218.

FIG. 2B shows a cross sectional view of a package in the process offabrication continuing from FIG. 2A. Since extended contact lead frameportion 212 provides additional space for contact under the packagecompared to contact lead frame portion 112 of FIG. 1E, two semiconductordevices 260 and 262 can be attached to the bottom of the package insteadof a single semiconductor device 160. Thus, semiconductor device 260,labeled Q1 (e.g. a first power transistor), is attached to the bottom ofpaddle portion 214 via electrical contact interface 266, andsemiconductor device 262, labeled Q2 (e.g. a second power transistor),is attached to the bottom of paddle portion 214 via electrical contactinterface 265. Semiconductor device 260 is also in direct electricalcontact with extended contact lead frame portion 212, and semiconductordevice 262 is also in direct electrical contact with extended contactlead frame portion 218. After attaching semiconductor devices 260 and262, the fabrication of the package is essentially complete and thepackage may then be attached on top of PCB 280 for integration usingelectrical contact interface 268 on the bottom surface of semiconductordevice 160 and electrical contact interface 269 on the bottom surface ofsemiconductor device 162.

As with FIG. 1F, the terminal assignments for interfaces 264 through 269may be flexibly arranged depending on various requirements. In oneembodiment, interfaces 264 and 267 may each be connected to a gateterminal, interfaces 268 and 265 may each be connected to a sourceterminal, and interfaces 266 and 269 may each be connected to a drainterminal. Semiconductor devices 260 and 262 are both electricallyconnected to semiconductor device 270 (U1) (e.g., a control IC), and maytherefore be controlled by voltages provided by semiconductor device270. Moreover, since semiconductor devices 260 and 262 both share thesame double-sided direct contact configuration as semiconductor device160 in FIG. 1F, similar packaging advantages such as improved currenthandling, thermal dissipation, reduced form factor and footprint, andimproved stability and reliability are achieved.

FIG. 3A shows a cross sectional view of a package in the process offabrication of still another embodiment of the present invention. Afabrication process as described above to achieve the package in FIG. 1Emay be used in a similar manner to fabricate the package in FIG. 3A.FIG. 3A provides an alternative embodiment for another exemplarypackage, which differs from FIG. 2A in that paddle portion 214 andattached semiconductor device 270 are replaced with two paddle portions314 and 316 with two attached semiconductor devices 370 (U1) (e.g., afirst control IC) and 372 (U2) (e.g., a second control IC),respectively.

The package in FIG. 3B may function in a similar manner as FIG. 2Bexcept that two separate semiconductor devices 370 and 372 controlsemiconductor devices 360 and 362 (which might be two powertransistors), rather than the single unified semiconductor device 270from FIG. 2B.

Thus, a direct contact leadless package and related structure and methodresulting in a semiconductor package especially suitable for highcurrent devices have been described to advantageously achieve, amongother things, low manufacturing cost, high current density handling,improved thermal dissipation, and reduced form factor and footprint. Themechanical structure of the invention's direct contact leadless packageprovides space for bottom-mounted semiconductor devices such as powertransistors for direct connection to the remaining lead frame portions.This direct and efficient connection allows the power transistors tohave direct contact from both sides: to a PCB on the bottom and to thelead frame portions on the top, allowing better conduction and heatdissipation enabled by large contact surface areas and short electricalroutes. Moreover, the invention's direct contact leadless package iscost effective since existing manufacturing process may be used.Moreover, the simplicity of the package structure allows for a reducedform factor and footprint, and contributes to stability and reliability,and avoids creation of high mechanical stress areas present inconventional packages.

From the above description of the invention it is manifest that varioustechniques can be used for implementing the concepts of the presentinvention without departing from its scope. Moreover, while theinvention has been described with specific reference to certainembodiments, a person of ordinary skills in the art would recognize thatchanges can be made in form and detail without departing from the spiritand the scope of the invention. As such, the described embodiments areto be considered in all respects as illustrative and not restrictive. Itshould also be understood that the invention is not limited to theparticular embodiments described herein, but is capable of manyrearrangements, modifications, and substitutions without departing fromthe scope of the invention.

1. A semiconductor package comprising: a first contact lead frameportion, a paddle portion, and an extended contact lead frame portionheld together by a mold compound; a first semiconductor device attachedto a top side of said paddle portion and enclosed by said mold compound;a second semiconductor device attached to a bottom side of said paddleportion and in electrical contact with said first semiconductor device;said extended contact lead frame portion being in direct electricalcontact with said second semiconductor device without using a bond wire;and a thickness of said paddle portion less than a thickness of saidfirst contact lead frame portion.
 2. The semiconductor package of claim1, further comprising a printed circuit board (PCB) attached to a bottomside of said second semiconductor device.
 3. The semiconductor packageof claim 1, wherein the first semiconductor device is a controlintegrated circuit (IC).
 4. The semiconductor package of claim 1,wherein the second semiconductor device is a power transistor.
 5. Thesemiconductor package of claim 4, wherein a gate terminal of said powertransistor is in direct electrical contact with said extended contactlead frame portion.
 6. A semiconductor package comprising: a firstcontact lead frame portion, a paddle portion, and an extended contactlead frame portion; a control IC attached to a top side of said paddleportion; a power transistor attached to a bottom side of said paddleportion and in electrical contact with said control IC; said extendedcontact lead frame portion being in direct electrical contact with saidpower transistor; and a thickness of said paddle portion less than athickness of said first contact lead frame portion.
 7. The semiconductorpackage of claim 6, further comprising a printed circuit board (PCB)attached to a bottom side of said power transistor.
 8. The semiconductorpackage of claim 6, wherein a gate terminal of said power transistor isin direct electrical contact with said extended contact lead frameportion.
 9. The semiconductor package of claim 6, wherein said firstcontact lead frame portion, said paddle portion, and said extendedcontact lead frame portion are held together by a mold compound.
 10. Thesemiconductor package of claim 9, wherein said control IC is attached tosaid top side of said paddle portion and is enclosed by said moldcompound.
 11. The semiconductor package of claim 6, wherein saidextended contact lead frame portion is in direct electrical contact withsaid power transistor without using a bond wire.
 12. The semiconductorpackage of claim 6, wherein said extended contact lead frame portion isin direct electrical contact with said power transistor without using aconductive clip.